The present invention relates to an inverter system which is, for example, used to drive and control a motor equipped in an electrically-driven compressor for an automotive vehicle.
An electric vehicle or a hybrid vehicle is generally equipped with two kinds of electric power sources, one of which is a low-voltage battery similar to that used in a gasoline vehicle and the other is a high-voltage battery insulated from the low-voltage battery. According to these automotive vehicles, an inverter system including an inverter operating under electric power supply of the high-voltage battery is provided for controlling a drive motor of the vehicle or a motor equipped in an electrically-driven compressor.
For example, the Japanese Patent Application Laid-open No. 11-189032(1999) corresponding to the U.S. Pat. No. 5,963,442 discloses an inverter system including an inverter 100 operating under electric power supply of a high-voltage battery 109 and an air-conditioning control section 104 operating under electric power supply of a low-voltage battery (not shown). An insulating communication circuit including a photo coupler 105 is provided on an insulation boundary between the air-conditioning control section 104 and the inverter 100. The photo coupler 105 has a function of insulating a low-voltage side electric component (such as the air-conditioning control section 104) from a high-voltage side electric component (such as a motor 106 or a switching element 107). Furthermore, the photo coupler 105 has a function of assuring communications between the air-conditioning control section 104 and the inverter 100. The communication protocol used for these communications is, for example, LIN (Local Interconnect Network) or other relatively low-speed communication protocol.
However, advanced automotive vehicles employ CAN (Controller Area Network) or other relatively higher-speed communication protocol, for example, for LAN communications between various ECUs (Electronic Control Units) installed in the vehicle.
According to the photo coupler 105 used in the above-described conventional inverter system, it is difficult to execute high-speed signal transmission between the air-conditioning control section 104 and the inverter 100. In this respect, as shown in FIG. 2, if a microcomputer 101 of the inverter 100 (indicated by a dotted line) is disposed at the low-voltage side of the insulation boundary (indicated by an alternate long and short dash line), more specifically when the microcomputer 101 operates under electric power supply of the low-voltage battery (not shown), it will be possible to execute high-speed communications.
However, in this case, some electric components such as a voltage detecting section 102, a gate driving circuit 103, and a current detecting section 108 will be dissected by the insulation boundary. Accordingly, in each electric component, there will be necessary to provide a sufficient spatial distance or creepage distance for assuring insulation between the high-voltage side and the low-voltage side. Furthermore, required insulation parts or components will be expensive. Accordingly, the body size of the inverter 100 will become large. Furthermore, incorporating the low-voltage battery in the inverter 100 will complicate the wiring of the inverter 100.